Alarm first-out circuitry



Oct. 21, 1969 e. E. LIGHTNER ET AL 3,474,443

ALARM FIRST-OUT CIRCUITRY Filed March 30, 1966 INVENTORS GENE E. LIGHTNER AND ATTORNEY United States Patent U5. Cl. 340-415 6 Claims ABSTRACT OF THE DISCLOSURE An alarm annunciator circuit for indicating abnormal conditions in monitored variables includes a first-out circuit for preventing actuation of any alarm indicators following actuation of the initial alarm indicator. Thereby, an indication of the first variable to become abnormal is preserved. For each variable to be monitored there is an individual indicator circuit which includes a visual indicator in series with the cathode-anode path of a silicon controlled rectifier responsive to the variable becoming abnormal to start conducting and provide energizing current to the visual indicator. Each of the indicator circuits is connected in common to a flasher circuit which causes the visual indicator associated with the conducting silicon controller rectifier to flash. A second common connection between all indicating circuits and a reference potential is provided to maintain a minimum current through the conducting silicon controlled rectifier when the flasher circuit periodically turns oil the associated visual indicator. An auxiliary silicon controlled 0 gized, and operates to connect the gate terminals of all 3 silicon controlled rectifiers in the indicating circuits to a source or potential which prevents the silicon controlled rectifiers from being turned on.

The present invention relates generally to electronic circuitry for an alarm annunciator, and more specifical- 1y to circuitry for indicating which one of a plurality of monitored devices attains an abnormal state before any other of such devices. Such alarm circuitry is commonly referred to in the art as first-out alarm annunciator circuitry.

In many control or monitoring systems, one abnormal condition will often result in a chain-reaction occurrence of a multiplicity of abnormal conditions. As a simple example, abnormally low oil level in a compressor bearing will result in a compressor shut-down, which in turn causes an abnormally low pressure to exist at the compressor. In most instances several sensing devices for detecting the occurrence of abnormal conditions are monitored in a single control room, where the abnormal conditions are indicated by indexed alarm annunciating equipment. For maintenance and supervisory reasons, it is often highly desirable to know which of the abnormal conditions occurred first. The present invention provides such first-out information reliably, at the speed of modern solid state electronic components, and yet at low cost.

Heretofore alarm annunciators of the general type have employed complicated logic circuits which include many expensive elements; for example AND gates, OR gates, and the like. Other types of alarm circuits have utilized mechanical relays in an attempt to provide the firstout feature. Although such circuits have served the purpose, they have not proved entirely satisfactory under all conditions of service for the reason that they have been susceptible to spurious signal triggering, relatively slow switching speeds and other related problems.

The general purpose of this invention is to provide alarm annunciator circuitry which embraces the firstout advantages of similarly employed annunciators, but yet does not possess the aforedescribed disadvantages. To attain this, the present invention utilizes a unique firstout circuit including a solid state control device, which, after the first indicating circuit has been actuated, positively prevents all other indicating circuits from being triggered to their actuated state.

An object of the present invention is the provision of a novel alarm annunciator circuit which assures that only the first-actuated indicating circuit of a plurality of such circuits remains in its actuated state upon the happening of some obnormal condition.

Another object is to provide an alarm annunciator consisting of a number of indicating circuits corresponding to the number of devices to be monitored, and wherein, until acknowledgment by an operator, the circuit provides an intermittent or flashing indication to draw attention to the first-actuated circuit.

A further object of the invention is the provision of alarm annunciator circuitry consisting of a plurality of independent indicating circuits controlled by a single first-out solid-state control circuit in common therewith.

A still further object of the invention is the provision of a first-out type alarm annunciator, wherein an operator may acknowledge an alarm indication and reset the first-out control circuit by means of a single acknowledgment switch.

In the present invention these purposes (as well as others apparent herein) are achieved generally by providing a plurality of indicating circuits which are electrically connected in parallel between the terminals of a power supply source. Each indicating circuit includes a unidirectional current control device, preferably a solid state silicon-control rectifier, having a gating terminal. The gating terminal is connectable to a source capable of providing a signal indicative of the occurrence of an abnormal condition at some monitored remote station. A second terminal of the control device is electrically coupled to one terminal of the two-terminal supply source and its remaining terminal is connected to two parallel circuits which are returned to the other terminal of the supply source. Each of the parallel circuits includes a junction terminal which is common to corresponding parallel circuits in the other indicating circuits.

An auxiliary solid-state unidirectional current device is provided to serve as the first-out control device. It has a gating terminal electrically coupled to one of the common terminals of a parallel circuit of the indicating circuits. Another of its terminals is connected to an auxilliary potential source, while its remaining terminal is coupled to the gating terminals of the control devices of the indicating circuits. When any one of the indicating circuits is actuated, the auxiliary control device is triggered to its conducting state. This allows the auxilliary potential source to be coupled to the gating terminals of the indicating circuit control devices, thereby to prevent triggering of these control devices after any one of them has been actuated.

Utilization of the invention will become apparent to those skilled in the art from the disclosures made in the following description of a preferred embodiment of the invention as illustrated in the acompanying drawing, in which:

The only figure of the drawing is a schematic diagram of the alarm annunciator circuit of the present invention, the ganged acknowledge switch being shown in its closed position and the dashed lines indicating its open position.

Referring now to the drawing, wherein like reference characters designate like or corresponding parts, there is shown in the drawing the alarm annunciator circuitry of the present invention. The alarm annunciator circuitry 10 consists of a plurality of indicating circuits, generally designated 12, connected in parallel between the terminals of a DC power supply 14. In the present invention the two-terminal power supply 14 has a positive terminal and a grounded terminal and is preferably rated at approximately 24 volts. It should be understood that although only two indicating circuits 12 and 12 are shown in the drawing additional indicating circuits 12", 12" etc., substantially identical to those shown, may be provided as desired. It is not uncommon, for example, to include as many as ten indicating circuits in a single alarm annunciator package.

Each of the indicating circuits 12 is comprised of an indication device 16 connected in series circuit with a control device 18. As shown in the drawing, the indication device 16 takes the form of an incandescent lamp, while the control device 18 is a solid state unidirectional current element, commonly referred to as a silicon-controlled rectifier (SCR). It should be apparent that a DC. operated horn or other indication device could be used instead of the lamp 16. One terminal of the incandescent lamp 16 is connected directly to the positive terminal of the two-terminal power supply 14 and its other terminal is connected to the anode electrode 26 of the control SCR 18. The SCR 18 is preferably biased so that it is normallynonconducting but switchable to its conducting state upon the application of a gating pulse, as more fully described hereinafter. The cathode electrode 22 of the control SCR 18 is connected at circuit point 24 to two parallel circuits which branch from the point 24 and converge at the grounded terminal of the power supply 14.

One of these parallel circuits includes a current-limiting resistor 26 whose one terminal is connected to the circuit point 24 and whose other terminal is connected to a junction terminal 28. The terminal 28 is common to all of the indicating circuits 12 and is connected to the grounded terminal of the power supply 14 by the acknowledgement contacts 30 and contact arm 32 of a ganged double-pole, single-throw switch, generally designated 34.

The other parallel circuit branching from circuit point 24 includes an isolation diode 36 whose anode electrode is connected directly to the circuit point 24 and Whose cathode electrode is connected directly to a junction terminal 38. The terminal 38 is common to all of the indicating circuits 12, but it is isolated from the cathode terminal 22 of each circuit by means of the isolation diodes 36. The common terminal 38 is coupled to the grounded terminal of the power supply 14 by means of an intermittently-operated flasher circuit, generally designated 40.

In essence the intermittent-flasher circuit 40 is an electronic switch circuit which includes an NPN transistor 42 whose collector electrode 44 is connected to the common junction terminal 38. The emitter electrode 46 of the transistor 42 is coupled to the ground terminal of the power supply 14 by means of a current-limiting resistor 48. The base electrode 50 of the transistor 42 is connected to a conventional oscillator circuit 52 which periodically and cyclically causes the transistor 42 to switch between its conducting and nonconducting modes of operation.

The alarm annunciator circuitry 10 is provided with input terminals 54 which are connectable by suitable leads (not shown) to the devices which provide the signals indicative of the occurrence of abnormal conditions at the remote stations. Each indicating circuit 12 has a separate input terminal 54 coupled to the gating terminal 56 of its control SCR 18 through a current-limiting resistor 58; the input terminals 54 further being connected to ground through a shunting resistor 60.

A solid state auxiliary control device, generally designated 62, is provided to ensure that only the first-actuated indicating circuit 12 will be actuated upon the occurrence of an abnormal signal at one of the monitored stations. Preferably the control device 62 is a unidirectional current device such as an SCR. In the present invention this first-out control SCR 62 has its gating terminal 64 connected to the collector electrode 44 of the transistor 42 by means of a series circuit including a diode 66, a coupling capacitor 68, and a current-limiting resistor 70. The diode 66 is poled such that its cathode is directly connected to the gating terminal 64 and its anode is connected to an auxiliary source of potential 72 by means of a resistor 74 and coupled to the collector 44 of the transistor 42 by the capacitor 68 and the resistor 70.

The particular value of the potential of the auxiliary source 72 is chosen such that, when applied to the gating terminals 56 of the control SCRs 18, it prohibits any input pulse or simultaneously applied signal from triggering the control devices 18 to their conducting states. The auxiliary potential source 72 is directly connected to the cathode electrode 76 of the auxiliary control SCR 62. The anode terminal 78 of this first-out control SCR 62 is connected to a common junction terminal 80 by means of the first-out reset contacts 82 and contact arm 84 of the switch 34. In turn, the terminal 80 is connected to the junction of a shunting resistor 86 and the cathode electrode of isolation diodes 88. The anode electrodes of the isolation diodes 88 are connected to the input terminals 54 of the respective indicating circuits 12. Thus, the auxiliary potential source 72 is coupled to the gating terminals 56 of the control SCRs 18 by the circuit including the resistors 58, the diodes 88, the reset switch contacts 82, and the anode-cathode path of the first-out control SCR 62.

To understand the operation of the alarm annunciator circuitry 10, assume that an abnormal condition has occured at some remote monitored station, thereby to provide an input signal in the form of a positive pulse to the input terminal 54 of the indicating circuit 12. The resistors 58 and 60 are chosen in accordance with the known magnitude of the input signal so that a pulse of approximately 0.50.7 volt is applied to the gating electrode 56 of the control SCR 18. Such a pulse is suflicient to trigger the control SCR 18 and it switches from its normally-nonconducting state to its conducting state. Thus, current is allowed to flow from the positive terminal of the power supply 14 through the indicating lamp 16, the anode-cathode path of the control SCR 18, to the circuit point 24. At circuit point 24 the current can flow either through the resistor 26 and the acknowledgment contacts 30 of the switch 34 to the grounded terminal of the power supply 14 or through the diode 36, the collector-emitter path of the transistor 42 to ground. This latter condition occurs only when the transistor 42 has been switched to its conducting state. When the oscillator 52 provides a sufliciently positive signal to the base electrode 50 of the NPN transistor 42, it is rendered conductive and substantially all current flow in the indicating circuit 12 is through the transistor 42 and the currentlimiting resistor 48 to ground. However, when the signal from the oscillator is such that the transistor 42 is turned off, as it will be during intermittent intervals, the current flow through the indicating circuit 12 will be through the resistor 26 and the acknowledgment conductors 30 of the switch 34 to ground. It should be noted that the parallel circuits including the resistor 26 is necessary to the proper operation of intermittently-operated flasher circuit 40; i.e. so that a flashing indication is observable at the indicating lamps 16. Without such parallel circuit arrangement, the current in the indicating circuit 12 would be reduced to a level (substantially zero) insufficient to sustain conduction of the control SCR 18 when transistor 42 is in its off cycle. This would defeat the purpose of utilizing SCRs as latching elements in the alarm annunciator circuitry 10.

When current flows through the indicating circuit 12 and the flasher-circuit transistor 42, a pulse is generated and coupled to the gating terminal 64 of the first-out control SCR 62 by means of the resistor 70, the coupling capacitor 68, and the diode 66. This triggering pulse actuates the control SCR 62 to switch it from its normallynonconducting state to its conducting state. In so doing the auxiliary potential source 72 is coupled to the gating terminals 56 of all of the control SCRs 18, 18' etc. by means of the circuits which includes the cathode-anode path of the first-out control SCR 62, the reset contacts 82 and arm 84 of the switch 34, the common terminal 80, the isolating diodes 88, and the current limiting resistors 58. Since the auxiliary potential source is chosen to be of a predetermined magnitude (in the present invention, approximately -3 volts), all of the control SCRs 18 are prevented from switching to their conducting state even though input signals are applied to their associated inputs 54.

The application of the auxiliary potential 72 to the gating terminal 56 of the first-actuated control device 18 does not adversely affect its operation. Once the control SCR has been switched to its conducting state it will continue to conduct until the current through its anodecathode path is reduced below its sustaining threshold level, as is well known in the art.

When an operator has noted the abnormal condition indication and taken steps to correct it, the alarm annunciator circuitry may be reset by simply opening the firstout reset contacts and the acknowledgment contacts of the switch 34. This open circuit reset operation interrupts the current flow through the first-out SCR 62, and the first-actuated control SCR 18 is returned to its nonconducting state. The contacts 30 and 82 of the switch 34 are then again closed and the alarm annunciator circuitry 10 is ready to detect and indicate the next occurrence of an abnormal condition at the stations being monitored.

Obviously, many modifications and variations of the present invention are possible in view of the above teach ings. For example instead of the SCRs disclosed hereinabove, circuits equivalent to an SCR such as the well known two-transistor Hook circuit or a vacuum tube thyration may be substituted without departing from the teachings of the present invention.

Also instead of the transistor 42 operating between its non-conducting state and a heavily conducting state, it may be biased between two discrete current conducting states. In this manner, the indicator lamp 16 of the indication circuit which is actuated will glow dimly in one state and more brightly in the other state. Therefore, it is to be understood that the invention may be practiced otherwise than as specifically described.

We claim:

1. Alarm circuitry for indicating which one of a plurality of monitored devices attains an abnormal state before other of such devices, comprising a two-terminal source of electrical energy,

a plurality of indicating circuits electrically connected to said two-termina'l source to receive electrical power therefrom, each indicating circuit including a unidirectional current control device having a first terminal serving as a gating terminal and a second terminal electrically coupled to one terminal of said two-terminal source, a third terminal being connected to first and second parallel circuits branching therefrom and being connected at opposite ends to first and second common terminals respectively, said common terminals being common to corresponding parallel circuits in the other of said indicating circuits, said control devices being normally in a nonconducting state but being switchable to a conducting state in response to a switching signal being applied to said gating terminal,

intermittently-operated switching circuit means connected between said first common terminal and said other terminal of said two terminal source of electrical energy for intermittently increasing and reducing the current flow from said first common terminal to ground when one of said current control devices is in the conducting state,

a circuit path between said second common terminal and ground for maintaining more than a predetermined minimum turn otf current through one of said current control devices which is in a conducting state, when said intermittently-operated switching means reduces the current flow from said first common terminal to ground,

an auxiliary potential source of a predetermined magnitude,

an auxiliary solid state unidirectional current control device having a gating terminal electrically coupled to said first common terminal, a second terminal of said auxiliary control device being connected to said auxiliary potential source, and a third terminal thereof being coupled to said gating terminals of said control devices of said indicating circuits,

whereby actuation of one of said indicating circuts triggers said auxiliary control device, thereby to apply said auxiliary source potential to said gating terminals of said indicating circuit control devices.

2. The alarm circuitry as defined in claim 1, wherein said unidirectional current control devices are siliconcontrolled rectifiers.

3. The alarm circuitry as defined in claim 1, wherein said circuit path comprises normally closed acknowledgement switching means connected to said second common terminal, whereby upon opening said switching means, any actuated indicating circuit is reset to its initial state of operation.

4. The alarm circuitry as defined in claim 3, further comprising first-out reset switching means connecting said auxiliary control device to said gating terminals of said control devices of said indicating circuits.

5. The alarm circuitry of claim 4, wherein said first parallel circuit of each indicating circuit includes a diode sufficient to electrically isolate its associated control device from said common terminal thereof, and

said other parallel circuit of each indicating circuit includes resistance means.

6. The alarm circuitry as defined in claim 5, wherein said first-out reset switching means and said acknowledgment switching means comprise a ganged doublepole, single-throw mechanical switch.

References Cited UNITED STATES PATENTS 3,029,421 4/1962 Beguin 340'415 3,147,464 9/ 1964 Spielman 340415 35813286 4/1968 Walsh 340-415 THOMAS B. HABECKER, Primary Examiner US. Cl. X.R. 307-252 

